Disconnect and Re-Connect Sync on the Problem Device This is a more thorough approach than just toggling the sync option. It forces Firefox to treat the device as new and perform a full initial sync. On the computer with the new motherboard, click the Firefox menu button (the three horizontal lines) and go to Settings. Click Sync in the left-hand menu. You should see your account email. Click the "Manage Account" button or the "Disconnect" button if it's visible. You'll be prompted to confirm. Choose to "Disconnect" or "Sign Out." This will delete the local sync data from that device (which is currently empty anyway). Restart Firefox. Click on the menu button again and choose "Sign in to Sync." Follow the on-screen prompts to sign back into your Firefox account. After signing in, Firefox should start a fresh sync and pull all the data, including payment methods, from your other devices that are still correctly synced.